FIG. 3. Hill plot of sNS binding to ssRNA to determine cooperativity. A gel shift assay with 0.24 pmol of radiolabeled 59S4-121 RNA was performed as described for Fig. 2A except that the concentrations of purified sNS ranged from 0.24 to 6 pmol. The amount of sNS bound at each concentration was calculated as described in Materials and Methods. Log10 (bound sNS/1 2 bound sNS) was plotted relative to log10 (sNS concentration), and a best-fit line was calculated for the linear portion of the graph (the equation and coefficient of determination for the line are shown in the box).